This invention relates generally to resilient tipped needle valves and, more particularly, to a needle valve having a simple conical rubber tip which is formed by grinding a molded rubber tip until a tip support is engaged.
Rubber tipped needle valves comprising generally conical rubber tips molded to rigid valve bodies are known in the prior art. The rubber tips are typically secured to the bodies by being molded to engage either sockets formed into the rigid bodies or mushroom-shaped projections, sometimes referred to as bayonets, extending therefrom. Difficulties have been encountered in the use of these valves primarily due to distortion of the rubber tip caused by shrinkage of the rubber after the tip is molded. Distortion of the molded rubber tip has been dealt with most effectively by grinding the conical end of the rubber tip.
In the prior art, rubber tips have been molded in a compound shape such that they can be ground without engaging the rigid valve bodies which are typically formed from metals including aluminum, brass, steel and stainless steel as well as various plastics. The compound shape, for example, can comprise a right cylindrical inner portion and an outer portion of truncated cone shape as shown in U.S. Pat. Nos. 2,414,577 and 3,440,313. Alternately, the inner portion may be formed as a conical section having a first apex angle and the outer portion formed as a conical section being a second apex angle which is greater than the first apex angle as shown in U.S. Pat. No. Re. 25,560. Preferably, the second apex angle is at or near the desired angle of the conical tip to be ground.
Such ground rubber tipped needle valves substantially overcome the problems associated with distortions of a molded rubber tip; however, they suffer from other shortcomings. For example, the use of a compound shaped tip, particularly the double angled configuration, reduces the maximum gauge or sealing diameter for a given valve body. In addition, grinding the end of a compound shaped tip can result in a cosmetic defect in the appearance of the needle valve.
The cosmetic defect results due to machining tolerances and because the distortion at the base of the molded rubber tip is nonuniform around the circumference of the base. Cylindrical tip retaining extensions, referred to as barrels, are machined at the end of the valve bodies. Machining tolerances result in the barrels being eccentric relative to the axis of the valve body. When the tip end is ground to the desired angle, the eccentricity of the barrel and the uneven distortion of the molded rubber tip make the unground base portion of the tip vary in width as one progresses around the valve. This varying width leads to the cosmetic defect which is an uneven banded appearance at the base of the tip.
While this uneven banded appearance does not affect the operation of the needle valve, upon visual examination it appears to be a defect which suggests improper concentricity of the conical rubber tip or an eccentric grind of the tip. Hence, such needle valves, although perfectly good, may be rejected as being defective.
Accordingly, the need exists for an improved rubber tipped needle valve which overcomes these problems and provides an increased gauge or sealing diameter for a given needle valve body.